This invention relates to a wet electrolyte valve-metal capacitor having a free-form encapsulant, and more particularly to such a capacitor that includes a sealed impregnation header.
It is known to make a wet electrolyte capacitor by encapsulating the dry capacitor section in a covering of epoxy or the like as by molding. Such molded coatings have a highly disciplined geometry that is particularly advantageous for producing axial leaded parts that are intended for automatic insertion into printed circuit boards. Such parts are typically provided with a tubular metal riser lead portion or lead eyelet through which the molded capacitor section is impregnated with electrolyte prior to sealing the eyelet and attaching a lead wire thereto. Examples of such capacitors are described by Brafman, U.S. Pat. No. 2,628,271 issued Feb. 10, 1953 and by Ness et al, U.S. Pat. No. 2,869,052 issued Jan. 13, 1959, both having the same assignee as the instant invention.
It is also known to make a wet electrolyte capacitor by coating a wet capacitor section with a reagent that seals the wet section and subsequently dip coating the protected wet section in epoxy followed by curing. Such a construction is described by Peck et al, U.S. Pat. No. 3,353,072 issued Nov. 14, 1969 and also assigned to the same assignee. This capacitor however is limited to the use of borate type electrolytes and requires an extra step in manufacture. It is not known to apply a wet or an uncured thermosetting resin coating directly to a wet capacitor section for two reasons.
The presence of a wet electrolyte adjacent to the uncured resin tends to inhibit curing, so at least the inner surface of the resin remains incompletely cured. Many resins and particularly most epoxies contain hydrolyzable chlorides, which in the partially cured resin interface are subject to a further chemical attack by the liquid electrolyte whereby chloride ions are released into the electrolyte. The chloride ions are highly corrosive to the valve-metal parts of the capacitor section and tend to greatly reduce the useful life of the capacitor, especially at elevated temperature and voltage.
Free-form encapsulants such as dip coats are known to be significantly less costly than molded or cast encapsulants, but a compatible method for introducing the electrolyte into a cured free-form coating while retaining the low cost advantages thereof has heretofore not been available.
It is therefore an object of the present invention to provide a low cost wet electrolyte valve-metal capacitor.
It is another object of the present invention to provide a wet electrolyte capacitor that is capable of being impregnated with an electrolyte and sealed after a free-form encapsulant is formed and cured.